1. Field of the Invention
The present invention relates to a process of preparing a hydrophobic or aerophilic powdered solid which is dispersible in water or in an aqueous solution (in the following referred to as a water dispersible solid) in the form of discrete microparticles.
2. The Prior Art
More specifically the invention relates to a process of preparing water dispersible hydrophobic or aerophilic powdered colorants and biologically active solids.
It is well known that the coloring effect of a colorant or pigment dispersed in an aqueous medium, increases with decreasing particle size of the colorant or pigment and that the color intensity of the dispersion increases with increasing dispersability.
It is also well known that the bioavailability of biologically active powdered solids, such as carotenoids and drugs, such as griseofulvin, ibuprofen, benzodiazepines and hormones, such as progesteron dispersed in an aqueous medium increases with decreasing particle size of the dispersed solid.
Therefore, there is a need for providing water dispersible hydrophobic or aerophilic solids of a small particle size, e.g., a particle size not exceeding 10 .mu.m, and more preferably not exceeding 2 .mu.m.
Various methods of reducing the particle size of hydrophobic/aerophilic compounds to a maximum average of 10 .mu.m have been disclosed. It is known to mill .beta.-carotene together with edible oil in a colloid mill (Chimia 21, 329 (67)). Using this method it is possible to achieve a .beta.-carotene content in the oil of about 30%.
Published Japanese patent application No. 57-3861 discloses a process for preparation of a water-dispersible carotenoid formulation which comprises mixing and grinding a carotenoid with gum arabic in a dry state using a grinding apparatus, such as rotary ball mills, vibration ball mills, and hammer mills. Following grinding the solid product can be dissolved in water and the resulting solution can be converted into a powder by spray drying or freeze drying. A powder formulation having a carotenoid content of 1.5 percent by weight is obtained. A disadvantage of this method is that the milled compounds may be damaged due to the increase of temperature during grinding or milling in the dry state because of the lack of efficient cooling equipment. Furthermore, it is difficult to prevent oxidation of the milled compounds during a dry grinding or milling operation.
Moreover, Chimia 21,329 (1967), DE application No. 12 11 911 and DE publication No. 25 34 091 disclose methods of dissolving the active compound in a chlorinated organic solvent, emulsifying the solution in a gelatine/sucrose solution and extracting the solvent from the emulsion causing the active compound to crystallize in microcrystalline form. A disadvantage of this method is that it is technically impossible to remove the organic solvent completely and the solvent is a potential hazard during the process and as residues in the final product.
DK-B-154.395 discloses a preparation, which has been prepared by dissolving a carotenoid or a retinoid in an organic solvent that is miscible with water at a temperature of between 50.degree. and 200.degree. C. optionally under pressure in less than 10 sec. The resulting molecular-disperse solution is immediately mixed with an aqueous solution of a hydrocolloid, followed by an isolation of the colloid-disperse particles from the solvent to obtain a dry free flowing powder that can be dispersed in water. This method is disadvantageous because of the use of organic solvents that require special equipment for collection of the solvents. Furthermore, the concentration of the active compound will be relatively low in the final product, i.e., a maximum of about 20 percent by weight. Furthermore, it is stated that it has not been possible to mill hydrophobic solids, such as .beta.-carotene in water or in an aqueous system to obtain the desired particle size without damage to the active compounds.
Research Disclosure (RD) 17064, June 1978, describes a method of preparing stable carotenoid colorants, wherein the carotenoids are milled in ball mills in an aqueous or oily medium in the presence of a protective colloid and a carrier, such as gelatine, and an ionic emulgator. The milling in the aqueous medium is followed by a spray drying process resulting in a water dispersible colorant having a carotenoid content of about 10%. However, the ionic emulgator will be present in the final product, which is undesirable especially when the colorant is to be used in food products.
It is well known that an aqueous dispersion of particles of hydrophobic/aerophilic solids can be prepared by mixing a hydrophobic/aerophilic solid with water in the presence of a wetting agent or tenside, such as lauryl sulfate or polysorbate. Without the use of a wetting agent milling is impossible, and without sufficient wetting the particles will agglomerate and the suspension will become too viscous for milling.